Digital controlled oscillator (DCO) circuits are used in a variety of applications such as phase locked loop (PLL) circuits to create alternating signals at a controlled frequency. Cross-coupled L-C oscillator circuits employ a tank circuit formed of an inductance and a parallel capacitance with a cross-coupled transistor pair to provide a differential alternating signal at a frequency controlled by adjusting the value of the tank circuit capacitance. DCO circuits provide an array of parallel-connected capacitor banks or cells with the ability to activate or deactivate individual cells to adjust the overall capacitance thereby providing frequency adjustment or tuning capability. Conventional DCO capacitor cells include circuitry to selectively connect two capacitances in parallel with the oscillator inductor to turn the cell “on”, with pull up transistor circuitry to help bias the floating terminals of the cell capacitors when the cell is turned “off”. At high frequency operation, however, drain-source resistive/capacitive impedances of PMOS pull up transistors in such conventional capacitor cells become more pronounced during the cell “off” state, whereby the phase noise is increased as the tank circuit impedance becomes more resistive. Accordingly, a need remains for improved DCO switchable capacitance circuitry for providing an alternating signal at a controlled adjustable frequency while mitigating phase noise.